How can you distinguish between a true flaw signal and surface roughness or tooling marks?

• A. Use a single high-frequency setting
• B. Use multiple frequencies and angles, compare with calibration references, and assess scaling with geometry and depth across scans
• C. Ignore signals near the surface
• D. Assume every echo is a flaw

Answer: (B)

Distinguishing a true flaw from surface roughness or tooling marks comes down to how the echo behaves when you change inspection conditions and compare to known references. A real internal flaw reflects the ultrasound in a way that aligns with its geometry and the material’s attenuation: the echo appears at a consistent depth (time-of-flight) and remains detectable across different probe frequencies and angles when you account for geometry and attenuation. By using multiple frequencies and angles, you can test whether the reflection persists and scales as expected with path length and orientation. If the signal truly comes from a defect, its behavior will follow the predictable attenuation and travel-time patterns dictated by the material and flaw geometry.

Surface roughness or tooling marks, on the other hand, are surface-related features. Their echoes are usually near the surface and can change markedly when you alter frequency or angle, often diminishing or shifting with different conditions. They do not exhibit the same depth scaling or consistent reflection characteristics as a through-thickness flaw. Calibrated references or phantom blocks with known defects help confirm whether a signal matches a real defect rather than a surface artifact, and looking at how the signal scales with geometry and depth across scans provides another check.

So, using multiple frequencies and angles, cross-checking against calibration references, and examining how the echo scales with geometry and depth collectively helps you distinguish a true flaw from surface roughness or tooling marks.